DESCRIPTION: (Adapted from abstract) Superoxide anion (SO) inhibits vascular relaxation and enhances vascular contraction. Although blood vessels possess the capacity to produce free radicals, including SO, the sources of SO are not clearly defined. The applicant's studies suggest that in normal rabbit aorta, a major source of SO production is unmasked by inhibition of endogenous superoxide dismutase. This SO is apparently derived from a novel enzymatic source which resembles but is distinct from neutrophil NADPH oxidase. The investigator has localized the activity within the membrane fraction of smooth muscle cells and adventitial cells, and has partially purified the protein. Preliminary data show that this source of SO is important in modulating vascular relaxation, since inhibition of SO production increases nitric oxide induced relaxations. A number of recent studies have shown an increased deleterious role of SO on the vasculature in angiotensin II (ANGII) hypertension and hypertension in general. More recently, a direct stimulation of this class of SO generating enzymes (NADH/NADPH oxidase) by angiotensin II (ANG II) was reported. The underlying hypothesis of this proposal is that ANGII dependent models of hypertension exhibit an increased activity and expression of the NADPH oxidase SO generating enzyme(s), which leads to increased SO generation and inhibits nitric oxide dependent relaxation and enhances endothelium dependent contraction contributing to the hypertension. This proposal will: (1) compare and contrast the vascular levels of SO and the activity and levels of the vascular NADPH oxidase source of SO in normotensive and ANG II-dependent and -independent hypertensive rabbits; (2) determine whether there is a contribution of NADPH oxidase derived SO to impaired relaxations and enhanced constrictions of blood vessels in ANG II- dependent hypertensive rabbits; (3) examine the effect of ANG II on NADPH oxidase levels and activity from cultured medial smooth muscle cells and adventitial cells. The proposed studies will determine whether ANG II and/or blood pressure elevation can stimulate the NADPH oxidase source of SO, and thereby exacerbate aberrant vascular tone.